Process for the production of 2, 6-dimethylnaphthalene



A. HAHN, JR

May 3, 1966 PROCESS FOR THE PRODUCTION OF 2.6-DIMETHYLNAPHTHALENE FiledMay 28. 1965 ATTORNEY United States Patent O 3,249,644 PROCESS FOR THEPRODUCTION F 2,6-DIMETHYLNAPHTHALENE Alfred Hahn, Jr., Brookhaven, Pa.,assigner to Sun @il Company, Philadelphia, Pa., a corporation of NewJersey Filed May 28, 1963, Ser. No. 283,772 4 Claims. (Cl. 26o- 668)naphthalenes, and in smaller quantity the ethylnaphthalenes. lRecyclefractions which are formed in the cracking of petroleum stocks and whichinclude this boiling ran-ge often include major proportions or aromatichydrocarbons that are mainly alkylnaphthalenes. Such fractions typicallyhave aromatic contents varying within the range of 25 %-97%, but usuallycontain between 50% and 95%, depending upon the particular operation inwhich` the petroleum fractions are produced. These hydrocarbon chargestocks are obtained in both catalytic and thermal cracking processes andin operations in which combinations of catalytic and thermal crackingsteps are utilized. Additionally, these hydrocarbon charge stocks canybe obtained as the reformate fraction from typical reforming processes,such as those using the well-known platinum catalyst. Stocks having highalkylnaphthalene contents can also be obtained by extractingstraight-run petroleum fractions of appropriate boiling ranges, such askerosene, -or by extracting the abovementioned cracked fractions, suchas catalytic ga-s oil, with suitable solvents, for example, furfural orsulfur dioxide, or 'by vselective adsorption using solid adsorbents,such as silica gel, activated carbon, molecular sieves, and the like.These aromatic concentrates may be composed of 100% aromatichydrocarbons.

The present invention is directed to the production of naphthalene and2,6-dimethylnaphthalene from petroleum hydrocarbon charge stocks of thetype referred to above. Basically the charge stock used in practicingthis invention is a petroleum hydrocarbon fraction boiling substantiallywithin the range of 400-900 F. and having an API gravity ranging from 540. Preferably the char-ge stock will boil between 450 and 550 F. andywill be composed by weight of 35 %-100% aromatic hydrocarbons includingsubstituted condensed-ring aromatics, such as alkylnaphthalenes and from65 %-0% non-aromatic type hydrocarbons. As used throughout thisdisclosure, alkyl and dialkyl are understood to be those radicals eachhaving at least one and no more than 6 carbon atoms, branched orunbranched, joined or conjoined. Also the alkyl radicals or groups willusually appear at Ithe a and positions on the naphthalene nucleus. Thistype of charge material also contains substantial amounts of sulfurcomponents that normally occur within this boiling range. Charge stocksmost typically employed have an aromatic content within the range of50%-95% by Weight and a sulfur content ranging from 1%-3%. In general,the substituted condensed-ring aromatic hydrocarbons constitute from 80%of the total aromatic type hydrocarbons present in the charge stock.

It has been proposed heretofore to prepare naphthalene by subjectingaromatic hydrocarbon stocks containing alkylnaphthalenes to hightemperature dealkylation in ICC the presence of hydrogen. As a generalrule, the dealkylation conditions employed can effect only a par-tialdealkylation in one pass of the alkylnaphthalenes through the reactor.In order to increase the yield of naphthalene, it is desirable tofractionate the reaction product to obtain the desired naphthaleneproduct, to recover another fraction comprising unconverted and onlypartially converted alkylnaphthalenes which is commonly recycled to thedealkylator to effect further conversion into naphthalene.

In the high temperature `dealkylation processes of the kind referred toabove, it is characteristic that alkyl groups in the ot position areremoved from the naphthalene nucleus at about twice the rate as thosealkyl groups in the position. Hence `the recycle fraction obtained fromthe reaction product contains considerably more -alkylnaphthalene thana-alkylnaphthalene. A typical composition of the recycle fraction is asfollows:

Percentl -methylnaphthalene 70 -methylnaphth-alene .'P. 15Dimethylnaphthalene 15 Based on the rates of demethylation of otandI-methylnaphthalenes, the dimethyl portion of the recycled stream willcontain 50%-70% by weight of a mixture comprisin-g 2,6- and2,7-dimethylnaphthalenes. According to the present invention thismaterial is utilized in a way to produce additional amounts ofnaphthalene and high purity 2,6-dimethylnaphthalene as an additionalproduct. The naphthalene is useful as the feed stock to processes whichmake Iphthalic anhydride or is useful alone as an insecticide. The2,6-dimethylnaphthalene is extremely usful a's an intermediate for theproduction of synthetic resins.

The invention is described more specifically With reference to theaccompanying drawing which is a schematic -flow sheet illustrating acombination but integrated process `for producing naphthalene and2,6-dimethylnaphthalene from petroleum charge stocks containingalkylnaphthalenes.

VReferring now to the drawing, the charge material which enters thesystem through line 10 is a catalytic gas oil fraction boiling in therange of 440-525 F. and lcontaining alkylnaphthalenes. Preferably, thefeed stock is a catalytic gas oil aromatic extract containing a majorproportion of dicytclic aromatics together with a minor proportion ofaromatics having only one aromatic ring 4and only a small amo-unt ofsaturated hydrocarbons. For example, a preferred charge stock maycontain -dicyclic aromatics, 35% monocyclic aromatics and 5% saturates.

The heated charge material together with hydrogen from line 46 passesthrough line 10 -to a catalytic desulfurizer 11 which contain-s adesulfurization catalyst 12 such as cobalt molybdenum on alumina ormolybdenum disulfide on alumina. The conditions for conducting thiscatalytic desulfurization and conditioning step include a temperaturewithin the range of 800-980 F.; pressure of l50-1000 p.s.i.g. with arange of 200-500 p.s.i.g. preferred; a hydrogen to hydrocarbon moleratio of 3:1 to 25:1, preferably 5:1 -to 15:1 and a liquid hourly spacevelocity of 0.5-10 (volumes of charge per hour per bulk Volume ofcatalyst). The hydrogen consumption under these condition-s should bebetween and 500 s.c.f. per barrel of liquid feed per percent sulfur inthe feed, and preferably between 200 and 400 s.c.f. per barrel. Thisconditioning step also effects cracking of most of the saturates andsome of the'monocyclic aromatic hydrocarbons. The sulfur, of course, isconverted mainly into hydrogen sulfide.

From desulfurizer 11 the reaction product is sent through line 13 tofractionator 14 from which normally gaseous components are removedoverhead through llne 15 and a C5 to 400 F. gasoline fraction is removedvia line 16. The 400 F. fraction which contains primarilyalkylnaphthalenes is removed through line 17.

Referring now to the high temperature dealkylation step, materialobtained as hereafter specified and composed mainly of monomethyl anddirnethylnaphthalenes and a small amount of ethylnaphthalenes passesthrough line 47 together with hydrogen introduced via line 45 intodealkylator 27. In the preferred embodiment of the invention thedealkylation reaction is effected thermally; that is, in the absence ofany catalytic material. The conditions for this thermal dealkylationinclude a pressure of 150-1000 p.s.i.g., preferably 200-500 p.s.i.g.; a

hydrogen to hydrocarbon mole ratio within the range of 3:1 to 25:1,preferably 5:1 to 15:1; a residence time of 2-300 seconds with apreferred residence time of 10-60 seconds; and a temperature above l000F., preferably within the .range ofl l200-1400 F., sufficient to effectdealkylation of alkylnaphthalenes. In this reaction only a partialdealkylation occurs since the alkyl groups which are in the a positionon the naphthalene nucleus are removed at about twice the rate as thosein the position. Hence the reaction product which leaves dealkylator 27through line 28 contains, in addition to the desired naphthalene,unreacted methylnaphthalenes and partially dealkylated naphthalenes.This mixture is enriched with respect to the -alkyl groups as comparedto the charge.

material fed to dealkylator 27.

In another embodiment of the invention, the dealkylation reaction whichis effected in dealkylator 27 canbe carried out catalytically utilizinga desulfurizing catalyst, such as cobalt molybdate or molybdenumdisulfide on alumina. Frequently the presence of catalyst in this ste-pfacilitates the dealkylation reaction, and in some cases permits it tobe carried out at a lower temperature than that required for thermaldealkylation. The catalyst also effects the conversion of any remainingsulfur into hydrogen sulfide and hence permits the preparation ofnaphthalene and 2,6-dimethylnaphthalene having a negligible sulfurcontent. The conditions for the catalytic dealkylation reaction includea pressure of 150-1000 psig-.with a range of 200-500 p.s.i.g. preferred;a hydrogen to hydrocarbon mole ratio of :1 to 25:1; a liquid hourlyspace velocity of 0.2-5.0; and a temperature above l000 F., usuallybetween 1100 F. and l200 F., suiicient to dealkylate thealkylnaphthalene hydrocarbons and convert any remaining sulfur mainlyinto hydrogen sulfide.

The reaction product from line 28 passes to fractionator 29 from whichgases and a C5-500 F. aromatic gasoline fraction are removed,respectively, from lines 30 and 31. Napthalene, as one desired product,is taken from line 32 as material boiling in the 400-450 F. boilingrange.

Typically, this fraction is composed predominantly of I naphthalene andhas a melting point of at least 78.6 Cl

and a sulfur content that is less than parts per million. -i

The 450 F. -lmaterial withdrawn from fractionator 29 via line 33 iscomposed mainly of monomethyl and dimethylnaphthalenes with the alkylgroups in the position predominatin'g. This stream also contains a smallamount of material boiling above the dimethylnaphthalenes whichdesirably should be removed. This material is passed through line 33 tofractionator 34 from which a monoalkylnaphthalene, such asmonomethylnaphthalene, concentrate boiling in the range of 450-500 F. isobtained overhead through line 36 and passed as hereinafter shown intodealkylator 27,V a dialkylnaphthalene, such as dimethylnaphthalene,concentrate boiling from 500-520 F. is removed through line 37, and thehigher boiling material is removed as bottoms via line 35.

The 500-520 F. fraction removed from fractionator 34 via line 37 isadmixed with the alkylnaphthalene containing material from line 17 andpassed into a fractionation section indicated by columns 18 and 22. Incolumn 18 material distilling below 500 F. and composed mainly ofmethylnaphthalenes and a small amount of ethylnaphthalenes is removedoverhead and passes through line 19 with other materials hereafterspecified to the dealkylator 27. Material boiling above 520 F. isrejected from the bottom of tower 18 via line 21, and an intermediatefraction boiling from 500-520 F. and composed of dimethylnaphthalenesand generally a small amount of ethylnaphthalenes is taken through line20 to tower 22.

In tower 22 the operating condition-s are adjusted to remove overhead inline 23 a 500-510 F. cut and removes'as a bottoms product a 5l0-520 F.boiling range fraction. It has beenfound that with sufficiently goodfractionation substantially all of 26- and 2,7-dimethylnaphthalenes thatwere present in the charge fraction will appear in the 500-510 F.overhead cut. fraction which is composed of vother dimethylnaphthalenes(mainly the 1,3-, 1,6- and 2,3-isomers) passes through lines 24 and 48in admixture with the 400-500 F. fraction in line 19 from tower 18 andother materials hereafter specified to dealkylator 27.

The 500-510 F. cut from line 23 will contain, in addition tosubstantially all of the 2,6- and 2,7-isomers, minor amounts of the1,3-, and1,6- and l,7-is omers, and generally a small amount ofethylnaphthalene. These other components all havel freezing pointsconsiderably Vlower than the 2,6- and 2,7-isomers hence; this cut istional crystallization. The 2,6- and 2,7-dimethylnaphthalene concentrateis removed from crystallizer 25 via line 38.4 The filtrate fromcrystall-izer 25 containing the other isomers, such as 1,3-, 1,6- and1,7-dimethylnaphthalenes is passed through line 26 and line 49 inadmixture with the material from lines 19, 24, and 36 through line 47together with hydrogen from line 45 into dealkylator 27.

The concentrate of 2,6- and 2,7dimethylnaphthalene from line 38 ispassed into a second crystallization zone containing crystallizer 39wherein the 2,6-isomer is separated from the 2,.'7-isomer by fractionalcrystallization. Pure 2,6-dimethylnaphthalene is recovered in high yieldthrough line 40. The 2,7-dimethylnaphthalene isomer is removed fromcrystallizer 39 via line 41.

The crystallization which takes place in crystallizer 39 to separate the2,6-isomer from the 2,7-isomer is performed, for example, by cooling asolution of the isomer 4concentrate from line 38 to a temperature in therange from 30 to 60 C. though higher temperatures can be used, e.g., upto I0 C. Normally the feed material from line 38 is dissolved in asolvent at room temperature, though higher temperatures can be employed,if desired, in order to reduce the amount of solvent needed. The solventratio is critical but will usually be in the range from 0.5-2.5 parts byvolume of solvent per part of hydrocarbon charge. Suitable solventsinclude the lower alcohols which are preferred. Aliphatic hydrocarbonscan be employed but relatively low temperatures should be used ifaliphatic hydrocarbons are employed. Mixtures of aliphatic hydrocarbonslin lower alcohols may also be employed. VAs a rule, a suitable solventshould be able to dissolve at least one gram of hydrocarbon per 10millimeters of solvent at 25 C. and must remain liquid at thecrystallization temperatures. Suitable aliphatic hydrocarbons includepropane, isobutane, n-pentane, nhexane, heptanes, etc.` Suitablealcohols include methanol, ethanol, isopropanol, n-butanol, amylalcohols, etc. The

amount of alcohol in the solvent is preferably in the range It is alsocontemplated that ketones, such as acetone,

A bottom methyl isobutyl ketone, etc., and the like can be substitutedfor, or usedV in conjunction with the alcohols. The solvents used can bethe same in the earlier and hereinafter specified latercrystallizations. The solvents used for washing filter cakes can be thesame as, or different from, the solvents used in the crystallization.Preferably, they are the same.

The concentrate of 2,6-dimethylnaphthalene which has crystallized fromthe cooled solution is filtered or otherwise separated from the solutioncontaining dissolved constituents of the original hydrocarbon fraction.Desirably, the filter cake is washed with solvents to remove adheringmother liquor, though it'his lis not necessary.

The filter cake of 2,6-dimethylnaphthalene is next heated in orde'r tomelt a portion thereof. The heating is` to .a temperature from 5 50 C.,more preferably `from 20-30 C. The melted hydrocarbons are then removedfrom the unmelted portion of the filter cake, which portion constitutesa 2,6-dimethylnaphthalene in high concentration. Typically, thisconcentrate has a melting point in the range from 50-75 C. However, itis still quite impure as may be seen from comparison with the meltingpoint of pure 2,6-dimethylnaphthalene. Advantageously the heating stepand the subsequent removal of melted material from the remaining solidsare performed on the same filter, or in the same centrifuge, etc., thatis used to separate crystals from mother liquor after the firstcrystallization. However, if desired, these steps can be performed inseparate heating and separation zones.

The amount of crystals which is melted is preferably in the range from5%-50% by weight of the total crystals. Lesser amounts usually do notprovide optimum purification 4of the 2,6-dime`t'hylnaphthalene, whilegreater amounts usually result in an undesirable extent of melting of2,6-dimeth'yl-naphthalene. However, in general, any substantial extentof fractional melt-ing will result in a desirable purification of theunmelted 2,6-dimethylnaphthalene.

The 2,6-dimethylnaphthalene concentrate obtained by removing meltedmaterial from the heating step is next recrystallized at a temperatureranging from -30 C.l

to -60 C. in the presence of a solvent.

The precipitated 2,6-dimethylnaphthalene is now removed byy filtration.The filter cake can be washed using cooled solvent, but this is notessential. Following the filtration at reduced temperature, the filteredcrystals are usually permitted to warm to room temperature. There may bea small amount of material in the crystals which melts during thisywarming, and this material may be removed by suction through the filter,aided by washing with cooled solvent, such as methanol, if desired, butsuch removal is not essential.

Therefore, the pure 2,6-dimethylnaphthalene which is in line 40 can beobtained by the following summary of processing steps:

1) The material in line 38 is dissolved, in say, npentane.

(2) The filter cake is heated to melt a portion thereof, and the meltedportion is separated from the unmelted portion by filtration. u

(3) The solution is cooled and filtered.

(4) The filter cake is Washed with, say, methanol, then recycled anddissolved in, say, n-pentane.

(5) The solution is cooled.

(6) The purified 2,6-dimethylnaphthalene is filtered from the pentanesolution. 5

(7) The 2,6-dimethylnaphthalene crystals are allowed to warm to roomtemperature, and if desired, any melted material is removed.

The 2,7-dimethylnaphthalene concentrate which is removed fromcrystallizer 39 is passed through line 41 into isomerizer 42. Inisomerizer 42 a catalytic isomerization reaction effects a transfer of asubstantial portion of the -alkyl groups to the a position. Thus,2,7-dimethylnaphthalene is converted into a mixture containing 2,6- and2,7-dimethylnaphthalenes. It should be noted, however, that thisisomerization reaction does not effect any shift of alkyl groups fromone of the aryl rings to the other in the same molecule although someamount 'of disproportionation between separate molecules may occur.Although the 2,7-dimethylnaphthalene is substantially converted to the2,6-isomer, other a-methylnaphthalenes, such as 1,5-, 1,6-, 1,7- and1,8- isomers may also be obtained.

One manner of effecting the isomerization in isomerizer 42 is to contactthe 2,7-dimethylnaphthalene with any solid, acidic, cracking catalyst,such as silica-alumina, silica-magnesia, silica-zirconia andacid-activated clays. The reaction temperature should be in the range of300 500 C., and preferably 400450 C. The liquid space velocity can varybetween 0.1 and 2.0 volumes of hydrocarbon per volume of catalyst perhour and more preferably is maintained inthe range of 0.5-6. It isdesirable to conduct the isomerization at a low pressure, generally inthe range of 0.05-0.5 atmosphere, as otherwise coking tends to occurrapidly with resultant deactivation of the catalyst. The low pressurecan be maintained either by holding a vacuum on isomerizer 42 or byintroducing an inert diluent along with the 2,7-dimethylnaphthalene,eg., nitrogen, hydrogen, methane, propane, butanes, and the like.Whenever the activity of the catalyst has dropped enough to requireregeneration, this can be done in conventional manner merely by flowingair through the hot catalyt to burn ofiP the coke deposits. Thereafterthe catalyst can be re-used for further isomerization.

Depending upon the conditions chosen for operating the isomerizationreaction, the isomerizate removed from isomerizer 42 via line 43 isrecycled in either of two ways. In one embodiment, if the isomerizationconditions are chosen so that the isomerizate in line 43 contains, forall practical purposes, only an equilibrium mixture of 2,6- and2,7dimethylnaphthalenes, the isomizate is recycled 4through lines 50 and38 into crystallizer 39 in said second crystallization zone forseparation of additional 2,6-di1nethylnaphthalene. Alternately inanother embodiment, if the isomerization conditions in isomerizer 42 arechosen so that substantial amounts of other dialkyl isomers areobtained, then the isomerizate is passed via line 44 through line 23into crystallizer 25 in said first crystallization zone whereinadditional 2,6- and 2,7-dimethylnaphthalenes are obtained.

I claim:

1. In a process involving,

( 1) hydrodesulfurizing a petroleum fraction boiling mainly in the rangeof 440-525 F. and containing mainly monocyclic and dicyclic aromatichydrocarbons including dimethylnaphthalenes,

(2) separating from the desulfurization product material containingalkylnaphthalenes,

(3) subjecting such material to a dealkylation reaction at a temperatureabove l000 F. to produce naphthalene and,

(4) recovering from the dealkylation product naphthalene and a fractionrich in monoalkylnaphthalene, the steps for producing and recovering2,6-dimethylnaphthalene which comprises:

(a) separating from the hydrodesulfurization product a fraction boilingessentially in the range of 500-510 F.,

(b) fractionally crystallizing in a first crystallization zone the500-510 F. fraction to separate 2,6- and 2,7-dimethylnaphthalene fromother dimethylnaphthalenes,

' (c) passing the filtrate from step (b), materials from step (a)boiling below 500 F. and above 510 F., and said fraction rich inmonoalkylnaphthalene to said dealkylation reaction for conversion tonaphthalene,

(d) fractionally crystallizing in a second crystallization zone the 2,6-and 2,7-dimethylnaphthalene product from step (b) to separate the 2,6-dimethylnaphthalene from the 2,7-dimethylnaphthalene, (e) recovering the2,6.-dimethylnaphthalene, (f) visomerizing the 2,7-dimethylnaphthalenefrom step (d) to a mixture rich in 2,6 and 2,7- dimethylnaphthalene,and, (g) recovering 2,6-dimethylnaphthalene from said mixture. 2.Process according to claim V1 wherein said mixture from step (f) isrecycled to said first crystallization zone. 3. Process according toclaim -1 wherein said mixture from step (f) is recycled to said secondcrystallization zone.

4. In a process involving,

(1) hydrodesulfurizing a petroleum fraction boiling mainly in the rangeof 440-525 F. and containing mainly monocyclic and dicyclic aromatichydrocarf bons including dimethylnaphthalenes,

(2) separating from the desulfurization product material containingalkylnaphthalenes,

(3) subjecting such material to a dealkylation reaction at a temperatureabove 1000 F..to produce naphthalene and,

(4) recovering from the dealkylation product naphthalene and a fractionrich in monoalkylnaphthalene, the steps for producing and recovering2,6-dimethylnaphthalene which comprises:

. (a) separating -from the hydrodesulfurization product a fractionboiling essentially in the range of 5005l0 F.,

(b) fractionally crystallizing in a rst crystallization zone the 500510F. fraction to separate 2,6- and 2,7-dimethylnaphthalene from otherdimethylnaphthalenes,

(c) passing the filtrate from step (b), materials 8, from step (a)boiling below 500 F. and above 510 F., and said fraction rich inmonoalkylnaphthalene to said dealkylation reaction for conversion tonaphthalene, i

(d) fractionally crystallizing in a second crystallization zone the 2,6-and 2,7-dimethylnaphtha- Iene product from step (b) to separate the 2,6-dimethylnaphthalene from the 2,7-dimethylnaphthalene,

(e) recovering the 2,6-dimethylnaphthalene,

(f) isomerizing the 2,7-dimethylnaphthalene from step (d) to a mixturerich in 2,6-dimethylnaphthalene by contacting said2,7-dimethylnaphthalenev with a solid, acidic, cracking catalyst,selected from the group consisting of silicaalumina, silica-magnesia,silica-zirconia and acid-activated .clays at a temperature in thev rangeof 300-500 C., a pressure in the range of 0.05-0.5 atmosphere, and aliquid hourly space velocity between 0.1 and 20 volumes of hydrocarbonper volume of catalyst per hour, and,

(g) recovering 2,6-dimethylnaphthalene.from said mixture.

References Cited by the Examiner UNITED STATES PATENTS DELBERT E. GANTZ,Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner. C. R. DAVIS, Assistant Examiner.

1. IN A PROCESS INVOLVING, (1) HYDRODESULFURIZING A PETROLEUM FRACTIONBOILING MAINLY IN THE RANGE OF 440*-525*F. AND CONTAINING MAINLYMONOCYCLIC AND DICYCLIC AROMATIC HYDROCARBONS INCLUDINGDIMETHYLNAPHTHALENES, (2) SEPARATING FROM THE DESULFURIZATION PRODUCTMATERIAL CONTAINING ALKYLNAPHTHALENES, (3) SUBJECTING SUCH MATERIAL TO ADEALKYLATION REACTION AT A TEMPERATURE ABOVE 1000*F. TO PRODUCENAPHTHALENE AND, (4) RECOVERING FROM THE DEALKYLATION PRODUCTNAPHTHALENE AND A FRACTION RICH IN MONOALKYLNAPHTHALENE, THE STEPS FORPRODUCING AND RECOVERING 2,6-DIMETHYLNAPHTHALENE WHICH COMPRISES: (A)SEPARATING FROM THE HYDRODESULFURIZATION PRODUCT A FRACTION BOILINGESSENTIALLY IN THE RANGE OF 500*-510*F., (B) FRACTIONALLY CRYSTALLIZINGIN A FIRST CRYSTALLIZATION ZONE THE 500*-510*F. FRACTION TO SEPARATE2,6- AND 2,7-DIMETHYLNAPHTHALENE FROM OTHER DIMETHYLNAPHTHALENES, (C)PASSING THE FILTRATE FROM STEP (B), MATERIALS FROM STEP (A) BOILINGBELOW 500*F. AND ABOVE 510*F., AND SAID FRACTION RICH INMONOALKYLNAPHTHALENE TO SAID DEALKYLATION REACTION FOR CONVERSION TONAPHTHALENE, (D) FRACTIONALLY CRYSTALLIZING IN A SECOND CRYSTALLIZATIONZONE THE 2,6- AND 2,7-DIMETHYLNAPHTHALENE PRODUCT FROM STEP (B) TOSEPARATE THE 2,6DIMETHYLNAPHTHALENE FROM THE 2,7-DIMETHYLNAPHTHALENE,(E) RECOVERING THE 2,6-DIMETHYLNAPHTHALENE, (F) ISOMERIZING THE2,7-DIMETHYLNAPHTHALENE FROM STEP (D) TO A MIXTURE RICH IN 2,6- AND2,7DIMETHYLNAPHTHALENE, AND, (G) RECOVERING 2,6-DIMETHYLNAPHTHALENE FROMSAID MIXTURE.